FEEDFORWARD ACTIVE-FILTER FOR OUTPUT RIPPLE CANCELLATION

An active filter for DC-DC converter ripple cancellation is described and demonstrated. The feed-forward technique used applies to any conve rter with an output filter inductor. The technique is inherently stabl e, performs in both continuous and discontinuous conduction modes, and applies to both square-wave and resonant converters. A suitable linea r amplifier, combined with a current transformer, implements it with l ow loss. An adaptive tuning scheme compensates for inductance variatio n and drift. Operation is demonstrated with buck, push-pull, and boost converter topologies. The result is output ripple below 10mV RMS, eff ective on converters with outputs as low as 2V and currents above 30 A .